From 60a1405eefec9d18e663604e2275c2b9b87f85e3 Mon Sep 17 00:00:00 2001
From: Clint Byrum <clint@fewbar.com>
Date: Tue, 30 Apr 2013 16:36:56 -0700
Subject: [PATCH] Use conditional GET to fetch latest ubuntu image.

This also switches to using curl which some people may not have
installed. However, curl is far superior for this type of download.

Change-Id: I7ac5a84b30eb8daad320c082f976931c41a24669
---
 .../ubuntu/root.d/10-cache-ubuntu-tarball     | 35 +++++++++++++------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/elements/ubuntu/root.d/10-cache-ubuntu-tarball b/elements/ubuntu/root.d/10-cache-ubuntu-tarball
index 76f02b3b..65d569b5 100755
--- a/elements/ubuntu/root.d/10-cache-ubuntu-tarball
+++ b/elements/ubuntu/root.d/10-cache-ubuntu-tarball
@@ -14,17 +14,32 @@ DIB_RELEASE=${DIB_RELEASE:-quantal}
 BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-$DIB_RELEASE-server-cloudimg-$ARCH-root.tar.gz}
 SHA256SUMS=${SHA256SUMS:-https://${DIB_CLOUD_IMAGES##http?(s)://}/$DIB_RELEASE/current/SHA256SUMS}
 
+cache_url()
+{
+    local url=$1
+    local dest=$2
+    local tmp=$(mktemp $(dirname $dest)/.download.XXXXXXXX)
+    rcode=$(curl -o $tmp -z $dest -w '%{http_code}' $url)
+    if [ "$rcode"  == "200" ] ; then
+        echo "Server copy has changed. Using server version of $url"
+        mv $tmp $dest
+    elif [ "$rcode" == "304" ] ; then
+        echo "Server copy has not changed. Using locally cached $url"
+        rm -f $tmp
+    else
+        echo "Server returned an unexpected response code. [$rcode]"
+        rm -f $tmp
+        return 1
+    fi
+}
+
 mkdir -p $IMG_PATH
-# TODO: don't cache -current forever.
-if [ ! -f $IMG_PATH/$BASE_IMAGE_FILE ] ; then
-   echo "Fetching Base Image"
-   wget $SHA256SUMS -O $IMG_PATH/SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH
-   wget $DIB_CLOUD_IMAGES/$DIB_RELEASE/current/$BASE_IMAGE_FILE -O $IMG_PATH/$BASE_IMAGE_FILE.tmp
-   pushd $IMG_PATH
-   awk "/$BASE_IMAGE_FILE/ { print \$0 \".tmp\" }" SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH | sha256sum --check -
-   popd
-   mv $IMG_PATH/$BASE_IMAGE_FILE.tmp $IMG_PATH/$BASE_IMAGE_FILE
-fi
+echo "Fetching Base Image"
+cache_url $SHA256SUMS $IMG_PATH/SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH
+cache_url $DIB_CLOUD_IMAGES/$DIB_RELEASE/current/$BASE_IMAGE_FILE $IMG_PATH/$BASE_IMAGE_FILE
+pushd $IMG_PATH
+grep "$BASE_IMAGE_FILE" SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH | sha256sum --check -
+popd
 # Extract the base image
 sudo tar -C $TARGET_ROOT -xzf $IMG_PATH/$BASE_IMAGE_FILE
 sudo rmdir $TARGET_ROOT/lost+found